Inflatable safety systems have gained wide use in vehicles, particularly automotive vehicles. Such inflatable systems restrain an occupant of the vehicle during an emergency situation by inflating a bag, that acts as a restraint mechanism to protect the occupant from injury. During operation, the bag is inflated by filling the bag with a gas that expands the bag a desired amount to satisfactorily restrain and protect the occupant.
The gas used to inflate the safety bag is typically provided by a device called an inflator. One type of inflator holds a highly pressurized gas that is allowed to expand into the bag to inflate the bag. A second type of inflator has a propellant material that chemically reacts in a combustion reaction to produce gases that inflate the bag. A third type of inflator uses a combination of gas production from a propellant material by chemical reaction and gas supplied from a pressurized gas source.
Desirable features of an inflator, from an economic standpoint, include (i) small size so that the inflator may be easily incorporated into the vehicle design; (ii) light weight so that the inflator does not detrimentally affect fuel efficiency of the vehicle, and (iii) the use of low cost materials and designs so that the inflator does not excessively impact the price of the vehicle. Important technical considerations include making sure that the inflator is capable of inflating the bag to a desired amount in a desired time and that gases used to fill the bag do not create a health or safety problem. For example, it is desirable to inflate the bag with gases that do not contain dangerous amounts of toxic materials, such as carbon monoxide and oxides of nitrogen, that could injure vehicle occupants. The gases also should not contain dangerous amounts of flammable materials, such as hydrogen, that could ignite and create a hazard for vehicle occupants. Furthermore, it is desirable that the gases not be smokey, because the presence of a smoke during an emergency situation tends to create confusion or panic among vehicle occupants even if the smoke is not itself harmful.
The use of a stored, pressurized gas in an inflator provides the advantage that it is easy to avoid the presence of toxic or otherwise unsafe gases. The use of such a stored gas in inflators is, however, generally uneconomic because the pressure vessels required to store the gas are bulky, heavy and expensive. Inflators using gas-generating propellant materials have the advantage that the inflators are less bulky, are smaller, weigh less, and are generally less expensive than inflators having a stored gas.
One disadvantage of using gas-generating propellants, however, is that many of the available propellants produce significant quantities of toxic gases, such as carbon monoxide, and/or flammable gases, such as hydrogen. Also, many propellant compositions contain metals that, upon combustion, form undesirable metal-containing particulates and/or condensables that can create undesirable smoke. It is generally required that undesirable particulates and/or condensables be filtered out of the gas prior to introduction of the gas into the bag. As used herein, a condensable is a component that is initially in a gaseous state with the propellant gases immediately following combustion of a gas-generating propellant material, but that is transformed into a liquid or solid form as the propellant gases cool. Also, many propellants have components that include a halogen, such as chlorine, that may form a combustion product that may be toxic or that may contribute to formation of undesirable particulates and/or condensables. Furthermore, many propellant materials are expensive and can add significantly to the cost of the inflator.
One method for reducing the amount of carbon monoxide and hydrogen produced by a gas-generating propellant is to use a hybrid inflator design, such as is described in any of co-pending U.S. patent application Ser. Nos. 08/210,668; 08/328,657 and 08/389,297, the contents of all of which are incorporated herein by reference in their entireties. In a hybrid inflator, both a stored, pressurized gas and a gas-generating propellant are used in order to reduce the aforementioned problems that have been encountered with the use of propellants alone. Although such hybrid inflators perform well, it would be desirable to avoid the complexity, bulk and cost associated with storage of a pressurized gas.
There exists a need for an improved inflator that avoids the cost, bulk and complexity of storing a pressurized gas and that is capable of delivering safe propellant gases to inflate an inflatable safety bag without the need for expensive designs, materials or equipment.